1. Field of the Invention
The present invention relates to a rotation angle detecting device which is applied to a rudder angle sensor for a car, and more specifically to an adjusting unit for a neutral position (a position where an absolute angle is 0°) in a rotation angle detecting device including a digital incremental-type rotation detecting unit which detects a rotation angle within 360° to output a digital code signal and an analog absolute-type rotation detecting unit which detects the number of rotations more than one rotation to output an analog signal.
2. Description of the Related Art
Conventionally, a technique is known in which a rotation angle detecting device is provided between a steering shaft and a chassis of a car so that the damping force of a suspension, the shift position of an automatic transmission, and steering of a rear wheel in a four-wheel steering car are controlled based on the steering angle, steering speed, and steering direction of a steering wheel which are detected by the rotation angle detecting device. In order to perform such control, a rotation angle over 360° needs to be detected. Therefore, a rotation angle detecting device capable of detecting an absolute angle is used.
As the rotation angle detecting device capable of detecting an absolute angle, a device is conventionally known which is constituted by a combination of an incremental-type rotation detecting unit for detecting a rotation angle within 360° and an absolute-type rotation detecting unit for detecting the number of rotations more than one rotation and which transmits the rotation of a rotor member constituting the incremental-type rotation detecting unit to a rotation ring constituting the absolute-type rotation detecting unit through a gear mechanism having a predetermined speed reduction ratio (for example, see Japanese Unexamined Patent Application Publication No. 10-227631).
The rotation angle detecting device disclosed in Japanese Unexamined Patent Application Publication No. 10-227631 includes an incremental-type rotation detecting device and an absolute-type rotation detecting device which are all digital types. However, instead of the rotation angle detecting device having such a constitution, a device is also known which is constituted by a combination of a digital incremental-type rotation detecting unit and an analog absolute-type rotation detecting unit which are all digital types. As the analog absolute-type rotation detecting unit, a unit is used which is constituted by a resistance board having a resistance pattern and a slider which is slidably brought into contact with the resistance pattern.
In this type of rotation angle detecting device which is used for controlling a car, the neutral position of a steering shaft needs to exactly coincide with the position of the rotation angle detecting device where an absolute angle is 0°, when the rotation angle detecting device is incorporated into a car. Therefore, in order that the rotation angle detecting device is easily incorporated into a car, the position of a signal detecting section with respect to a rotating section, such as the rotor section or the rotation ring, is set to the position where an absolute angle is 0°, and the rotating section and the signal detecting section are required to be fixed to the position, when the rotation angle detecting device is shipped.
In order to fix the position of the signal detecting section with respect to the rotating section to the position where an absolute angle is 0°, the following method is used. Pin insertion holes having the same diameter are respectively formed in predetermined positions of a housing and the rotating section constituting the rotation angle detecting device, that is, in the positions where the signal detecting section and the rotating section face each other in a state where the position of the rotating section with respect to the signal detecting section is adjusted to the position where an absolute angle is 0°. After the rotation angle detecting device is assembled, a fixing pin passes through the respective pin insertion holes.
When a car is assembled, the rotation angle detecting device is assembled into a steering shaft or the like in a state where the fixing pin has passed through the respective pin insertion holes. After a car is assembled, the fixing pin is pulled out, so that the steering shaft can be rotated. Accordingly, the neutral position of the steering shaft when a car is assembled and the position of the rotation angle detecting device where an absolute angle is 0° do not need to be adjusted, which makes it easy to assemble a car.
In the meantime, in the rotation angle detecting device for a car including the analog absolute-type rotation detecting device, an output voltage value of the absolute-type rotation detecting device is required to be set in the strict range of 2.5±0.05 V, for example, in a state where an absolute angle is 0°.
However, the output voltage value of the analog absolute-type rotation detecting device is determined by the contact position of the slider with respect to the resistance pattern when the fixing pin passes through the respective pin insertion holes formed in the housing and the rotating section, and the voltage value is varied by a forming error of the resistance pattern and an assembling error of the resistance board into the housing. Therefore, it is hard to obtain an output voltage value in the above-described strict range, even though forming precision of the resistance pattern and assembling precision of the resistance board into the housing are designed to be enhanced. For this reason, in the related art, a method is adopted in which an output voltage value of an absolute-type rotation detecting device is examined after assembling, and then only an absolute-type rotation detecting device whose output voltage is determined to be proper is shipped.
As such, the conventional rotation angle detecting device is not provided with a unit for adjusting an output voltage value of an absolute-type rotation detecting section during assembling, so that only rotation angle detecting devices having a good quality are selectively shipped. Therefore, the manufacturing yield is lowered, and a rotation angle detecting device becomes expensive.
Moreover, if an output voltage adjusting unit, such as a variable resistor, is incorporated into a rotation angle detecting device, the manufacturing yield can be improved. However, the number of components increases, and an assembling operation becomes complicated, which makes it difficult to obtain an effect of a reduction in cost.